Cross equatorial transport in the Indian Ocean
Tommy Jensen, IPRC
The difference in net freshwater flux into the Bay of Bengal (BB) and into the Arabian Sea causes large differences in their salinity. A net evaporation over the Arabian Sea requires an exchange its high salinity with lower salinity water. Likewise, the Bay of Bengal must replace part of its low salinity water with higher salinity water from the south.
Model simulations with a 4.5 layer, 1/3 deg. resolution Indian Ocean model, based on the Thermodynamic Ocean Modelling System (TOMS), are used to investigate the exchanges between these two marginal seas and their exchanges with the central Indian Ocean. The model is forced with ECMWF climatological winds and restoring to Levitus surface SST and SSS. It is demonstrated, using passive tracers released into the Arabian Sea and the Bay of Bengal, that an important part of the required exchanges for the two seas involves cross-equatorial transports. Low salinity flux into the Arabian Sea occurs in the western boundary from the Somali Current, while its high salinity water is released into the Bay of Bengal and into the central Indian Ocean, across the equator. The Bay of Bengal exports its low salinity water to the southern hemisphere along the eastern boundary of the Indian Ocean. The cross-equatorial changes have a strong annual cycle, with maximum transports during the southwest Monsoon. In the annual mean, a Sverdrup driven southward equatorial transport occurs in the interior Indian Ocean, with compensating northward transports at intermediate depths in the central Indian Ocean and along the western boundary.
Finally, it is briefly discussed how models that include bottom topography, and are fully eddy resolving may improve upon our understanding of cross-equatorial transports in the Indian Ocean.
